1. Field of the Invention
The present invention relates to a controller for an AC rotary machine and a controller for electric power steering capable of reducing the amount of operation while maintaining the reliability in current control against disturbance.
2. Background Art
In control of an AC rotary machine, the reference frame of a current or a voltage which is the vector quantity may be divided into approximately two kinds of the reference frames, that is, the stationary reference frame and the rotating reference frame.
As examples of the stationary reference frame, the three-phase AC reference frame which directly treat the values of three phases, for example, U, V, and W phases and the two-phase reference frame which observe a state on the orthogonal two-axis stationary reference frame by three-phase/two-phase conversion are known.
As the rotating reference frame, orthogonal rotating two-axis reference frame are known well. In addition, the rotating reference frame which rotate in synchronization with the rotation position of an AC rotary machine, the rotating reference frame which rotate in synchronization with a frequency command, and the rotating reference frame which rotate in synchronization with the estimated magnetic flux of a rotor or an induced voltage are known as examples of the rotating reference frame.
In the related art, a controller for an AC rotary machine that gives a current command value on the rotating reference frame and performs control such that the current of the AC rotary machine matches the current command value when driving the AC rotary machine is known.
For example, in a known controller for an AC rotary machine disclosed in JP60-219984A (page 2, FIG. 1), a detection current on the stationary reference frame acquired from a current detector is converted into a detection current on the rotating reference frame on the basis of operational expression for reference frame transformation, and a voltage command on the rotating reference frame is controlled such that the converted current matches the current command value on the rotating reference frame. Moreover, a voltage command on the rotating reference frame is converted into three-phase voltage commands on the stationary reference frame on the basis of operational expression for reference frame transformation, and the AC rotary machine is controlled on the basis of the three-phase voltage commands.
Moreover, for example, in a known controller for an AC rotary machine disclosed in JP2-285966A (page 2, FIG. 2), three-phase detection currents of an AC rotary machine detected by a current detector are converted into two-phase currents, which are perpendicular to each other, by a three-phase/two-phase converter and then a detection current on the rotating reference frame is calculated by a reference frame transformer. The deviation between the set current command on the rotating reference frame and the set detection current on the rotating reference frame is calculated separately for each axis, integral control of the deviation between the current command on the rotating reference frame and the detection current on the rotating reference frame calculated separately for each axis is performed by two sets of integrators such that the input deviation becomes zero, and the result is output as a voltage command on the rotating reference frame. Two-phase voltage command values perpendicular to each other on the stationary reference frame are output by reference frame transformation of the voltage command on the rotating reference frame, and the two-phase voltage command values are converted into three-phase voltage command values by two-phase/three-phase conversion. On the other hand, the current command value on the rotating reference frame set by a current setting device is converted into three-phase current command values by reference frame transformation and two-phase/three-phase conversion, and three-phase voltage commands are output by three sets of proportional control on the deviation between the three-phase current commands and the three-phase detection currents. Three sets of adders add the three-phase voltage command values, which are obtained by converting the two-phase voltage command values, and the three-phase voltage command values, which are obtained by three sets of proportional control, for each phase, and the AC rotary machine is controlled on the basis of three-phase voltage command values obtained as a result of the addition.
Moreover, for example, a known controller for an AC rotary machine disclosed in JP11-018469A (paragraphs 0025 and 0067 to 0079, FIG. 13) includes: a feed forward signal calculating means for outputting a current command before one sampling period, which is a current command on the rotating reference frame axis of an AC motor, as a model current and for outputting a model voltage proportional to the rate of temporal change of the model current; a current control means to which a deviation between the model current and a current on the rotating reference frame is input and which outputs a compensation voltage; and an adding means for adding the model voltage and the compensation voltage and outputting a voltage command on the rotating reference frame. Therefore, since a problem is solved in which overshoot of a step response increases if a response frequency is set high in order to obtain the current control performance of high-speed response, high-speed current control response is realized.
In the case of using a controller for an AC rotary machine for electric power steering and the like, highly reliable current control performance against disturbance caused by variation in the power supply voltage is desirable. In order to maintain the highly reliable current control performance against disturbance, proportional operation in the current control is important and it is preferable to set the operation period of proportional operation short.
In the known controller for an AC rotary machine disclosed in JP60-219984A, if the operation period of proportional operation is set short, there is a problem that the load of operation performed by a microcomputer and the like increases because the proportional operation in current control is performed on the rotating reference frame and accordingly, an operation for reference frame transformation also needs to be executed in a short period.
Moreover, in the known controller for an AC rotary machine disclosed in JP2-285966A, reference frame transformation from a current command on the rotating reference frame to a current command on the stationary reference frame is required in addition to the reference frame transformation from a detection current on the stationary reference frame to a detection current on the rotating reference frame and the reference frame transformation from a voltage command on the rotating reference frame to a voltage command on the stationary reference frame. Accordingly, since the number of times of reference frame transformation is larger than that in the controller for an AC rotary machine disclosed in JP60-219984A, there is a problem that the load of operation performed by a microcomputer and the like increases.
Moreover, in the known controller for an AC rotary machine disclosed in JP11-018469A, the following capability of a current with respect to a current command can be improved using the feed forward signal calculating means, but the reliability of current control against disturbance caused by variation in the power supply voltage is the same as that in the controller for an AC rotary machine disclosed in JP60-219984A. That is, in order to maintain the reliability of current control, the operation period of proportional operation is set short. For this reason, there has been a problem that the load of operation performed by a microcomputer and the like increases like the controller for an AC rotary machine disclosed in JP60-219984A.